Study On Structure And Properties Of Melt-spinning Polyurethane Filament

As one of the rapidly developing synthetic fibers, polyurethane(PU)also named spandex, is usually blended with polyester, cotton and wool or made into covering yarn used in the textiles. The outstanding elasticity of the polyurethane could endow the yarns,fabrics and garments with good elasticity with only a few addition of spandex. Therefore there were more and more fabrics mixed with polyurethanes to improve the comfortability and wear-ability of the textiles.Scanning electron microscope(SEM), infrared spectroscope(FTIR), X-ray diffractometer(XRD), differential thermogravimetry and thermogravimetric analysis(DTA-TG) and single yarn electronic strength tester were used to investigate the morphological structure, aggregation structure and properties of the polyurethanes. At the mean time, the factory dyeing process(pretreatment, pre-heat setting, dyeing, post-heat setting) were simulated during the experiments and the strength and recovery rate of the treated filaments were tested by the electronic single yarn strength tester. Considering the demand on low temperature dyeing of spandex blended with polyester, the benzyl alcohol and the o-vanillin were chosen as the auxiliaries of disperse dyeing. Meanwhile, the acid dyes and the cationic dyes were chosen to dye the melt-spinning polyurethanes according to the structure of PU.The results shows as follows: the cross section of the melt-spinning polyurethanes is near to circular structure which is different from the dry-spinning polyurethane with a dumbbell shape; the breaking strength of the dry-spinning polyurethane was smaller than the melt-spinning polyurethanes but with a higher elastic recovery rate and breaking elongation rate. The mechanical properties of the melt-spinning polyurethanes were effected distinctly by thermal treatment. When the filaments were gone through different thermal treatment, the thermal stability order is PD520J>PD520H>dry-spinning PU; theX-ray diffraction peaks were not changed obviously. The process of pre-treatment, the pre-heat setting and the post steam heat-setting in the experiment were determined:T=90℃,Na2CO3=0.2g/L; t=30min, T=180℃; t=60s, T=175℃,t=30s., respectively.The benzyl alcohol was a better choice than the o-vanillin during low temperature dyeing of polyester with different structures of disperse dyes, and the optimum dosage was20ml/L. Although the dyeing up-take were increased, the homochromy could not be reached. The dyeing rate and the dyeing percentage of the spandex was superior to the polyester during high temperature and high pressure dyeing process with different structures of disperse dyes. The melt-spinning polyurethanes dyed with acid dyes could obtain over 90% of dyeing up-take, while the melt-spinning polyurethanes were hardly dyed with the cationic dyes.